Performance Issue on Mackbook air after OS update

Hello kisnahp,

Thank you for using Apple Support Communities! I understand that you have some concerns with the performance of your MacBook Air after upgrading to macOS Catalina. It's also taking longer for your Mac to start up, and to switch between user accounts. I would be happy to help provide steps to take so your Mac is running at peak performance again.

To help us further isolate potential causes of this behavior, I would like to have you check the following:

1. Go to System Preferences > Security & Privacy > FileVault. Do you see an indication that FileVault is currently encrypting your drive?
2. When the Mac performs slowly after you have logged in, what does your CPU activity look like? See how apps affect Mac performance, battery runtime, temperature, and fan activity - Apple Support
3. Let's also restart your Mac in macOS recovery, then run First Aid on your startup disk: Repair a storage device in Disk Utility on Mac - Apple Support
4. Next, restart the Mac in safe mode and test if there's a change in performance: Use safe mode to isolate issues with your Mac - Apple Support

Keep us posted on the results.

Cheers!

I suggest that you run an EtreCheck report and post it here so that we can assist you with the potential reasons that your notebook is performing poorly.

Ref: Using EtreCheck to Troubleshoot Potential… - Apple Community

Here are some observations/suggestions, based on the EtreCheck report:

1. Your notebook is RAM limited. 8 GB is apparently not enough to run multiple applications that you are using simultaneously. You can tell this by looking at the "Virtual Memory Information" section of the report. Notice that the "Swap Used" is not zero. That means, that your notebook is using some of its drive space to temporarily store applications in use. This will slow down their performance. Suggestion: Either upgrade the amount of RAM or do not run as many apps concurrently.
2. Google apps, like Chrome, tend to be memory "hogs." If you like using Chrome vs. Safari, I suggest that you try the Opera browser. It is built on the same Chromium engine, but does not come with the memory overhead that Chrome does.
3. Completely remove CCleaner. "Cleaner" apps are not required by macOS. They tend to cause more issues than solve them.
4. If you are running a VM manager ... looks like you use Virtual Box, know that it requires a fair amount of RAM to provide to a VM. Again, with your notebook's limited amount of RAM, when running a VM, there will be a significant performance hit.
5. Unless you really need them, remove any remote access apps: MeetingJoin, WebEx, etc.
6. Are you using a Bluetooth audio device? Headset, speakers, etc.? If so, when you ran the report, it was using a considerable amount of available CPU processing.
7. Finally the Diagnostics section indicates that, again, Bluetooth processing is causing high CPU usage. Your notebook also experienced a crash of the VLC app.

You can determine which apps on your Mac are 32-bit by doing the following:

1. Hold down the <option> key, and then, click on the Apple logo on the macOS menubar.
2. Select "System Information."
3. In the left-pane, select "Applications" under the "Software" category.
4. It will take a minute or so for each of the apps on your Mac to be listed.
5. Select an app, and then, look at the value for "Kind." It will either be 64- or 32-bit.